Fluorination, and Tunneling across Molecular Junctions

다국어 초록 (Multilingual Abstract)

<P>This paper describes the influence of the substitution of fluorine for hydrogen on the rate of charge transport by hole tunneling through junctions of the form Ag<SUP>TS</SUP>O<SUB>2</SUB>C(CH<SUB>2</SUB>)<SUB><I>n</I></SUB>(CF<SUB>2</SUB>)<SUB><I>m</I></SUB>T//Ga<SUB>2</SUB>O<SUB>3</SUB>/EGaIn, where T is methyl (CH<SUB>3</SUB>) or trifluoromethyl (CF<SUB>3</SUB>). Alkanoate-based self-assembled monolayers (SAMs) having perfluorinated groups (R<SUP>F</SUP>) show current densities that are lower (by factors of 20–30) than those of the homologous hydrocarbons (R<SUP>H</SUP>), while the attenuation factors of the simplified Simmons equation for methylene (β = (1.05？±？0.02)<I>n</I><SUB>CH<SUB>2</SUB></SUB><SUP>–1</SUP>) and difluoromethylene (β = (1.15？±？0.02)<I>n</I><SUB>CF<SUB>2</SUB></SUB><SUP>–1</SUP>) are similar (although the value for (CF<SUB>2</SUB>)<SUB><I>n</I></SUB> is statistically significantly larger). A comparative study focusing on the terminal fluorine substituents in SAMs of ω-tolyl- and -phenyl-alkanoates suggests that the C–F//Ga<SUB>2</SUB>O<SUB>3</SUB> interface is responsible for the lower tunneling currents for CF<SUB>3</SUB>. The decrease in the rate of charge transport in SAMs with R<SUP>F</SUP> groups (relative to homologous R<SUP>H</SUP> groups) is plausibly due to an increase in the height of the tunneling barrier at the T//Ga<SUB>2</SUB>O<SUB>3</SUB> interface, and/or to weak van der Waals interactions at that interface.</P><P><B>Graphic Abstract</B>
<IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-11/jacs.5b00137/production/images/medium/ja-2015-001374_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b00137'>ACS Electronic Supporting Info</A></P>